Actually the thick aluminum would work very well on low bass which might be more why it is used? Low bass just flexes the cabinet panels at a wide band of frequencies if they aren't super stiff. . This isn't resonance, just movement. Unless the panels are super stiff, and the 1" thick Aluminum would be super stiff.
Id love to be able to use 1" thick Al for speakers...a bit too heavy for anything other than very small bookshelf designs unfortunately. Though a ply-Al-MDF lam would be interesting....
I have a fair chunk of 8" square aluminum tube with 1/2" walls. Cut a couple lengths out and cap the ends.
dave
Make the bracing distance proportional to the thickness in comparison to plywood and MDF and I think you will see just how stiff sheet metal is...
It's important to put things in context and on an equal plane for comparison - equal thicknesses of MDF and plywood with equal bracing has the MDF deflecting more because it is less stiff.
When a plate deflects, it is working to dissipate the energy it took to make it deflect in the first place, therefore it is damping that energy.
In this instance I am talking about deflection in the form of vibration from the sound energy.
Like "resonance", I see a lot of different ideas as to what "constrained layer" construction is. My understanding of constrained layer is that it is 2 layers - an inner layer and an outer layer, the outer layer usually being significantly thicker than the inner layer. These layers are coupled together with a lossy medium - a layer of adhesive that allows the inner layer to deflect and vibrate (thereby dissipating energy) without transferring this energy to the outer layer.
Following that definition, MDF and plywood are not constrained layer on their own.
This is where I believe constrained layer construction beats out Dave's method - it dissipates more of the internal energy, especially if it is properly constructed.
Like comparing a room with concrete walls, ceiling and floor and how reverberant it is inside in comparison to that same room lined with walls built just slightly away from the concrete - a huge difference in reverberation. These walls are absorbing and dissipating much of the sound energy.
That would be a waste of 1" aluminum...
Try this: A sandwich of thin aluminum (or steel) sheets, inner and outer rigidly adhered to a 1/2" or 3/4" MDF core (depends on the panel span). This would would be very stiff.
Now, add another layer of aluminum sheet inside, but couple it to the sandwich with a rubbery layer, like silicone. Viola! Constrained layer.
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This however says nothing about damping really. While it is true that EVENTUALLY the panel will come to rest, it's deflection is not a useful metric. You can have to materials that exhibit the same amount of deflection under load but have very different characteristics for damping.
In this instance I am talking about deflection in the form of vibration from the sound energy.
You are being a bit too literal. I'm saying that if the panel deflects (vibrates), it will damp some of the vibration - how much is not important. It is the movement of the panel that is dissipating the energy.
A stiffer panel will move less to the same amount of energy, therefore under equal physical circumstances it will damp less.
I think I siad the density will go up a little (very very little) as the molecules move every so slightly closer together.
I agree that if a surface is "making" or producing or generating sound (acting like a speaker) then it has to be displacing air and moving in a measurable manner.
If however it is transmitting sound, the compression/rarefaction waves are passing through the material and the movement is on a molecular level and we can't measure it. I guess this is still movement of the surface though.
The question then becomes :
Wich material or combinations of material will cause the exterior surface molecules to move the least over a range of frequencies?
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and the answer is:...
no single material. A composite is the only way, in my opinion.
@MJL: i have some mild steel 'shims' that i may just try silicone-ing to the inner surface, the only physical coupling being the silicone rubber. This is what i call CLD. i dont believe it is true CLD if the panels are more attached than this. right or wrong i dont know lol
no single material. A composite is the only way, in my opinion.
@MJL: i have some mild steel 'shims' that i may just try silicone-ing to the inner surface, the only physical coupling being the silicone rubber. This is what i call CLD. i dont believe it is true CLD if the panels are more attached than this. right or wrong i dont know lol
Home Depot sells rolls of thin aluminium that are 10" wide (if memory serves) which would be easy to cut to size.
Hi,
That's roof flashing - maybe 22 gauge and not really thick enough for this. You'd want at least 16 gauge for some rigidity. Steel would be a better choice as it is much stiffer than aluminum and on the inside it wouldn't "ruin" the appearance.
Without correct definitions this is going to be pointless.
Here is a moderately helpful piece:
http://www.earsc.com/pdfs/engineering/CLD.pdf
Here's one we can sell as a tweak!
http://www.epsginc.com/data/cldm.PDF
Here is a moderately helpful piece:
http://www.earsc.com/pdfs/engineering/CLD.pdf
Here's one we can sell as a tweak!
http://www.epsginc.com/data/cldm.PDF
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That is basically the same as I described it - my lossy medium (silicone) is the damping layer in their illustration.
I'm no molecular physicist but I am pretty sure that any sound coming from the cabinet of your speaker is NOT a molecular level effect. Those cabinet molecules will have to move a lot, on a molecular scale, to transmit any sound. With my limited knowledge and experience in this field, I think I can claim that any sound that comes from your cabinet is due to vibrations of the cabinet, either induced from the sound waves inside the cabinet, or from the vibration of the case of the element that is attached to the speaker.
Thicker is better. If 22 gauge is 0.0253" and 16 gauge is 0.0503", based on the graph below, for a 1" composite panel (foam filled) the flexural rigidity values are about 120,000 and 230,000 respectively. The best plywood would come in at about 165,000 for 1" thick but is way heavier. This is why aorplanes are built out of these kind of panels.
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Hi pietschu,
Where do you find all of this data? You are good with the research
I knew a metal skinned sandwich was stiff but I had no idea it was that much stiffer than a comparable thickness of plywood - wow!
Wheels are turning...
The ducting sheet metal is rather thin also, unless it is a large piece (the bigger the duct, the thicker the material). You can get a better deal on better material directly from a sheet metal shop - a Google search for sheet metal sales should give you a few local choices. They can quickly shear it to the rough size you need also.
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